| 摘要 |
PURPOSE:To reduce the influence of damping when a sector reaches the aimed aperture by providing an aperture value setting means setting the aimed aperture value corresponding to a manual operation or field brightness, an exposure time setting means setting the aimed exposure time corresponding to the manual operation or the field brightness. CONSTITUTION:A driving pulse generating means supplies a driving pulse in an opening direction with respect to a step motor 10. When a pulse time when the step motor 10 rotates the sectors 2 and 3 up to a phase having strong holding power just before they are opened up to the aimed aperture value is relatively extended compared with a pulse time in a sector opening region before it, on the process, braking force for maintaining a step rotary position acts on the step motor 10 at that time. Therefore, the step motor rotates from the step rotary position to the aimed step one, the sectors 2 and 3 and the inertial force of a transmission line are greatly reduced. Thus, when the sectors 2 and 3 reach the aimed aperture value, damping is reduced. |
